The present invention pertains to an improved drop detection method and apparatus. More particularly, the present invention is directed to a method and apparatus for indirectly detecting fluid drops as they are collected in a drip chamber by piezoelectric means. A direct sensing method is disclosed in Ser. No. 564,997 filed concurrently herewith, entitled Direct Piezoelectric Drop Counter, assigned to the assignee herein, and incorporated herein by reference.
The invention is contemplated specifically for use in the administration of parenteral solutions to patients in hospitals and the like, but it also can be utilized for detecting and controlling drop flow of any liquid in precise quantities over a desired period of time into chemical or biological reactors, industrial processes, and the like.
While the administration of parenteral solutions is a common practice in hospitals, and great quantities of equipment of many different types are sold for the purpose of providing such administration, in many instances the medical situation calls for the administration of precisely controlled amounts of medication on a continuous drip basis over a period which may last several days or weeks. Cancer chemotherapy agents, for example, may be administered in this manner.
For these agents, and for many other medications, they must, of course, be administered to the patient in sufficient quantities to be effective, and often a uniform, continuous low volume dose is required. At the same time, an accidental increase in the flow rate can be life threatening in the case of some medications, and thus must be totally avoided.
The drop flow from conventional, gravity-operated parenteral solution equipment can vary widely, because of a range of variable situations that can occur, such as head height changes, patient blood pressure changes and changes in the controlling orifice due to tubing cold flow. These and other effects can cause intermittent or widely varying drop flow.
In the prior art, numerous patents exist which suggest various systems for controlling the flow of parenteral solution through a large assortment of electronic devices which purportedly provide improved flow accuracy. As a typical example of such prior art, drops of the solution are formed and fall through a conventional drip chamber in an administration set and are detected as they fall by a drop detector which can operate on photometric principles, by sensing variations in capacitance, or the like. A flow control clamp valve or other occlusion device is provided in the flow conduit and is controlled by a feedback mechanism, typically electronic, for sensing the drop rate in the drip chamber and appropriately controlling the valve so that the drop rate is kept within desired parameters.
In the prior art, a pump often is used to propel the solution through the set. This carries its own hierarchy of risks, and requires the presence of safety systems to prevent the pumping of air into the patient in the event that the source of parenteral solution runs dry. Such safety systems are, of course, subject to breakdown and failure, and the consequences of that also potentially are fatal.
It therefore is preferable, for safety and simplicity, to utilize a gravity operated system which measures amounts of parenteral solution to a patient. The utilization of the prior photometric drop detectors can cause numerous problems. The photometric or electro-optic detectors generally are relatively expensive, are easily misaligned, are easily damaged, such as by falling off the drip chamber, have large power requirements and otherwise can cause a variety of operational problems. The prior detectors also do not determine the volume of the fluid drops sensed.